- Radiation length
In physics, the

**radiation length**is a characteristic of a material, related to the energy loss of high energy, electromagnetic-interacting particles with it.**Definition**High-energy

electrons predominantly lose energy in matterbybremsstrahlung , and high-energyphotons by SubatomicParticle|AntielectronSubatomicParticle|Electron pair production. The characteristicamount of matter traversed for these related interactions is called the radiation length X_{0},usually measured in $gcm^\{-2\}$. It is both the mean distance over which a high-energyelectron loses all but 1/e of its energy by bremsstrahlung, and 7/9 of the mean freepath for pair production by a high-energy photon. It is also the appropriate scale length for describing high-energy electromagnetic cascades.The radiation length is given, to good approximation, by the expression

$X\_0\; =\; frac\{716.4cdot\; A\}\{Z\; (Z+1)\; ln\{frac\{287\}\{sqrt\{Z;gcdot\; cm^\{-2\}$. [

*cite book| last=Eidelman| first=S.| title=Review of Particle Physics*]where Z is the

atomic number and A is themass number .For electrons at lower energies (below few tens of

MeV s), the energy loss byionization is predominant.While this definition may also be used for other electromagnetic interacting particles beyond

lepton s and photons, the presence of the stronger hadronic and nuclear interaction makes it a far less interesting characterisation of the material; thenuclear collision length andnuclear interaction length are more relevant.Comprehensive tables for radiation lengths and other properties of materials are available from http://pdg.lbl.gov/AtomicNuclearProperties

**ee also***

Mean free path

*Attenuation length

*Attenuation coefficient

*Attenuation

*Range (particle radiation)

*Stopping power (particle radiation)

*Electron energy loss spectroscopy **References***S. Eidelman "et al."

Particle Data Group , "Review of particle physics", Phys. Lett. B**592**(2004) (http://pdg.lbl.gov/)

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